A self-starting permanent magnet synchronous motor operates as an inductor motor at the time of starting thereof owing to a starter squirrel cage conductor and as a synchronous motor as rotating magnetic poles created by the permanent magnets are entrained by a rotating magnetic field formed by a stator winding and moving angularly at a synchronous speed upon arrival of the rotor at a speed approaching the synchronous speed. This synchronous motor has an excellent constant speed operating performance and an excellent high efficiency. In particular, various improvement have hitherto been made to a rotor structure of the synchronous motor.
For example, the Japanese Patent Publications No. 59-23179 and No. 63-20105 discloses the prior art rotor structure for the self-starting permanent magnet synchronous motor.
FIG. 6 illustrates the prior art rotor disclosed in the Japanese Patent Publication No. 59-23179. Referring to FIG. 6, reference numeral 1 represents a rotor, and reference numeral 2 represents a rotor iron core having a plurality of slots 3 defined therein adjacent an outer periphery thereof. Conductor bars 4 are disposed within those slots 3 and have their opposite ends shortcircuited by respective shortcircuit rings to thereby form a starter squirrel cage conductor. The shortcircuit rings (not shown) are made of an annular electroconductive material disposed on axially opposite ends of the rotor iron core and are connected with the conductor bars 4. A plurality of magnet retaining holes 5 are provided on an inner side of the conductor bars 4, with corresponding permanent magnets 6 embedded therein. Reference numeral 7 represents magnetic flux shortcircuit preventive slits that are spaced such a small distance P from the magnet retaining holes 5 that magnetic saturation can take place between the magnet retaining holes 5 and the slits 7 to thereby prevent the magnetic fluxes emanating from the permanent magnets from being shortcircuited between the different magnetic poles.
FIG. 58 illustrates a longitudinal sectional view of the rotor used in the prior art self-starting synchronous motor disclosed in the Japanese Patent Publication No. 63-20105 and FIG. 59 illustrates a cross-sectional view taken along the line A-A′ in FIG. 58. Referring to FIGS. 58 and 59, reference numeral 11 represents a rotor, and reference numeral 12 represents a rotor iron core made up of a laminate of electromagnetic steel plates. Reference numeral 13 represents conductor bars having their opposite ends connected with respective shortcircuit rings 14 to thereby form a starter squirrel cage conductor. Reference numeral 15 represents permanent magnets embedded in the rotor iron core to form four rotor magnetic poles. Reference numeral 16 represents magnetic flux shortcircuit preventive slits each operable to prevent the magnetic fluxed between the neighboring permanent magnets of the different polarities from being shortcircuited. Reference numeral 17 represents an end plate disposed on each of axially opposite ends of the rotor iron core 2 by means of bolts to avoid any possible separation of the permanent magnets 5 from the rotor iron core 2.
When the prior art permanent magnet motor of the type provided with the cage conductor is to be used since the conductor bars and the permanent magnets are employed as rotatory drive elements, if the conductor bars and the permanent magnets are incorrectly positioned relative to each other, a force generated from the conductor bars and a force generated by the permanent magnets will be counteracted with each other and, therefore, no efficient rotatory drive will be achieved. Also, the permanent magnet motor provided with such a cage conductor requires a complicated and increased number of manufacturing steps since the permanent magnets and the conductor bars are provided in the rotor.
In view of the foregoing, the present invention is intended to solve those problems inherent in the prior art permanent magnet synchronous motor and is to increase the efficiency and simplify the manufacture of the synchronous motor of the type employing the permanent magnets.